The present invention relates to an electrophotographic sensitive member comprising a photoconductive amorphous silicon carbide layer.
Recently, the progress of the electrophotographic sensitive member is remarkable and various kinds of characteristic have been required for also a photosensitive member itself with the development of a copying machine, a printer and the like carrying the photosensitive member thereon.
An amorphous silicon layer has been watched with interest for this requirement on account of its superiority in heat resistance, abrasion resistance, antipollution property, photosensitive characteristic and the like.
However, the amorphous silicon layer (hereinafter called a-Si for short) has a dark resistance of merely about 10.sup.9 .OMEGA..multidot.cm if it contains no impurity as a dopant and in the case where it is used in the electrophotographic sensitive member, it is necessary to give the dark resistance of 10.sup.12 .OMEGA..multidot.cm or more, whereby enhancing a charge-retentivity. To that end, boron and the like have been added but no sufficiently satisfactory dark resistance bas been obtained, that is, merely a dark resistance of about 10.sup.11 .OMEGA..multidot.cm has been obtained.
On the other hand, a multi-layer type photosensitive member comprising an a-Si photoconductive layer and other non-photoconductive layer overlapped on said a-Si photoconductive layer has been proposed with the development of the above described dopants.
For example, FIG. 1 shows such a multi-layer type photosensitive member comprising a substrate (1) and a barrier layer (2), and a-Si photoconductive layer (3) and a surface protective layer (4) formed on said substrate (1) in this order.
With this multi-layer type photosensitive member, the barrier layer (2) aims at the prevention of carriers from entering from the substrate (1) and the surface protective layer (4) aims at the protection of the a-Si photoconductive layer (3) to improve the moisture resistance and the like but both layers (2), (4) aim at the increase of the dark resistance of the photosensitive member to enhance the charge acceptance. Accordingly, it is not required to make these layers photoelectrically conductive.
As above described, the conventional well-known a-Si photosensitive member is characterized by that a photocarrier-generating layer is formed of the a-Si photoconductive layer, whereby having superior advantages in heat resistance, durability, photosensitivity characteristic and the like but on the contrary it has an insufficient dark resistance, and accordingly, the dopants have been used and the dark resistance has been enhanced by forming a multi-layer type photosensitive member. That is to say, the barrier layer (2) and the surface protective layer (4) formed in the multi-layer type photosensitive member aim at the elimination of the disadvantages incidental to the a-Si photoconductive layer itself, and accordingly, it can be said that the are the layers which can be substantially discriminated from the a-Si photoconductive layer (3).
In view of the above described circumstances, the present inventors have already found that amorphous silicon carbide (hereinafter called a-SiC for short) has the photoelectric conductivity and its dark resistance easily amounts to 10.sup.13 .OMEGA..multidot.cm or more regardless of the existence of the dopants, and besides, it can form an electrophotographic sensitive member which can be positively and negatively charged by the selection of the dopants.
It is the reason why the above described a-SiC layer could form the electrophotographic sensitive member that the a-SiC layer has a large carrier-mobility and a dark conductivity of 10.sup.-13 (.OMEGA..multidot.cm).sup.-1 or less, whereby the large charge acceptance could be obtained.
However, still more superior electrophotographic characteristics are desired even for the a-SiC electrophotographic sensitive member having such a large carrier-mobility with the progress of the development of instruments on which the photosensitive member is placed. For example, in the case where the photosensitive characteristics can not sufficiently meet the use required, the background smearing occurs on the image and the residual potential is increased.